1. Field of the Invention
The present invention relates to a map display apparatus that is capable of displaying road information or the like as a bird's-eye view map in the bird's eye view format obtained by looking down diagonally at a map in a specific direction from above.
2. Description of the Prior Art
There are map display apparatuses for vehicles in the prior art that display a road map on a display device in the so called bird's-eye view display format, whereby a road map in the vicinity of the current position of the vehicle is displayed magnified compared to portions of the map in the distance (refer to U.S. Pat. No. 5,161,886, for instance). The apparatus disclosed in the above-mentioned application sets a viewpoint to the rear of the current position of the vehicle and displays the road state on the ground from this viewpoint looking down in the advancing direction of the vehicle on a screen of a display device. In such a bird's-eye view display, map information in the vicinity of the current vehicle position can be displayed enlarged, and in addition, since a wide range of area from the current position to distant positions can be displayed, it is easy to visually read route connections on the road map. Another advantage is achieved when the display direction, i.e., the direction in which the road map is looked down upon, is set to match the advancing direction of the vehicle, in that intersections and the like on the path of the vehicle's advance can be observed in detail, making the road map very easy to see when the path of advance is a linear path.
However, in a road display employing the bird's-eye view format, the closer to the position of the viewpoint, the more magnified is the display of the road map becomes and, at the same time, the range of the road map displayed on the screen is reduced. Since the current position of the vehicle is near the viewpoint, only a limited range in the vehicle advancing direction is displayed for the vicinity of the current vehicle position and, as a result, the road map in the vicinity of the current vehicle position cannot be studied thoroughly.